Preparation Of Lignin-based Hydrogel And Study On Low Temperature Resistant Supercapacitors Performance

The increasing popularity of portable/wearable multifunctional electronic devices has increasingly strict requirements on the stability and durability of new energy storage devices.The hydrogel electrolytes possess dual functions of electrolyte and separator,and have advantages of good flexibility,adjustable mechanical properties and high safety.Moreover,a large number of pore structures also provide effective ion transport channels,further improving the electrochemical performance,making the hydrogel electrolyte become one of the most ideal substitutes for various electrolytes in electrochemical energy storage devices.However,traditional hydrogel electrolytes have poor mechanical strength and are prone to serious deterioration or even deactivation when the operating temperature is too low.Therefore,in this paper,a low-temperature resistant hydrogel was prepared by using low-cost corn straw lignin as the matrix material,and systematically studied its structure,mechanical properties,and the electrochemical performance of the supercapacitor constructed by the hydrogel electrolyte.The main research contents are as follows:（1）A multifunctional hydrogel with flexibility,adhesion and low-temperature-resistant was prepared by alkali-catalyzed ring-opening polymerization of lignin and gelatin with polyethylene glycol diglycidyl ether（PEGDE）.The hydrogel exhibits excellent resilience and has a maximum elongation at a break of 260%.Lignin/gelatin hydrogel displayed good adhesion to different substrate surfaces.The ionic conductivity of the hydrogel electrolyte at room temperature reaches 0.065 S cm^-1.The supercapacitor prepared by the hydrogel electrolyte provides a specific capacitance of 145.14 F g^-1at a current density of 0.5 A g^-1,and even can work normally under compression and bending conditions.The supercapacitor also shows good low temperature performance:the specific capacitance can reach 110.56 F g^-1(0.5A g^-1)at-40°C,which is about 76.2%of that at room temperature.（2）In order to further improve the mechanical properties of lignin hydrogel and the electrochemical properties of the hydrogel electrolyte,an inorganic nanoparticle-reinforced double-network hydrogel was constructed.The hydrogel has high elongation at break（275%）and Young’s modulus（0.04 MPa）.An appropriate amount of nano-silica can improve the ionic conductivity of the hydrogel electrolyte,and its ionic conductivity at room temperature can reach 0.096 S cm^-1.The energy density of the supercapacitor constructed by it can reach 6.25W h kg^-1at a current density of 1.0 A g^-1.The hydrogel can still withstand different mechanical deformation at-30°C,and the supercapacitor also has excellent electrochemical performance at low temperature:SC-10%AM-3%Si O₂can still provide a high specific capacitance of 150 F g^-1(1.0 A g^-1)at-30°C,which is about 80%of that at room temperature.（3）The dynamic redox system composed of activated modified lignin and metal ions is used to activate the initiator to generate free radicals,and then initiates the polymerization of monomers at room temperature to form double cross-linked hydrogels.Fe³⁺in the hydrogel chelated with carboxylate to form a dynamic covalent bond.Lignin molecules are uniformly dispersed in the hydrogel and play an enhanced role.The synergistic effect of physical and chemical crosslinking ensures good stability of the hydrogel.The double crosslinked hydrogel has excellent mechanical properties and fatigue resistance,and the elongation at break can be as high as 700%.The hydrogel electrolyte has a high ionic conductivity of 0.345 S cm^-1at room temperature,and the supercapacitor prepared by it can provide a high specific capacitance of 210 F g^-1(1.0 A g^-1).Moreover,the hydrogel electrolyte can not only be used in an alkaline environment but also exhibit good electrochemical performance under neutral and acidic conditions.The ionic conductivity reaches 0.044 S cm^-1at-40°C.At the same time,the hydrogel also has good sensing performance,and the sensitivity is 1.34 within 100%strain.It can be used as a wearable sensing device to monitor the activity of human joints.